This invention relates to a process for the continuous firing of powdered carbon and an apparatus therefor. More particularly, it relates to a process for firing powdered carbon continuously by the application of microwaves and an apparatus therefor.
Conventionally, in order to graphitize powdered carbon by firing, a furnace 20 illustrated in FIG. 6, which is called an Acheson furnace, has been used. First of all, a large number of graphite containers 21 are filled with a raw material comprising powdered carbon, arranged in furnace 20, and completely covered with a large amount of packing coke 22. After a heat shield lining 23 is placed around packing coke 22, containers 21 within furnace are collectively heated by passing an electric current therethrough for several days, so that the powdered carbon is raised in temperature and thereby fired. Thereafter, containers 21 are cooled by allowing them to radiate heat spontaneously over a period of several weeks. In this figure, reference numeral 24 designates furnace walls made of fire bricks; 25, graphite terminal electrodes; and 26, busbars.
Furnace 20 included in the above-described conventional firing apparatus is a heating furnace of the so-called batch type in which a firing operation cannot be started before the preceding one is completed.
As a result, this firing process involves the following problems.
(1) In the course of firing, components other than the fired product, i.e. packing coke 22 and heat shield lining 23 surrounding containers 21 within furnace 20, are concurrently heated together with the fired product, and thereafter cooled together with the fired product. This results in low thermal efficiency and hence an increased unit cost of electric power used for production.
(2) It takes several weeks to carry out the heating and firing step and the cooling step. If the operating time required for filling containers with powdered carbon and embedding these containers and the operating time required for taking out the containers are added thereto, it takes about one month to finish each firing operation for graphitization. This makes it difficult to meet a demand for increased production of powdered carbon.
(3) This firing process involves environmentally severe dusty operations such as the operation for filling with packing coke. Accordingly, even if one or more additional Acheson furnaces are installed in order to meet a demand for increased production of powdered carbon, it is difficult to secure personnel sufficient for the firing operation.
Consequently, the conventional firing process using an Acheson furnace has been unable to meet satisfactorily the demand of the battery market for increased production of powdered carbon which will hereafter be expected owing, for example, to the increased use of lithium batteries.
The present invention has been made in view of the above-described existing state of the art, and an object thereof is to provide a process for the continuous firing of powdered carbon which involves high thermal efficiency, can satisfactorily meet a demand for increased production of powdered carbon, and can be carried out with less operating personnel, as well as an apparatus therefor.
That is, in one aspect, the present invention provides a process for the continuous firing of powdered carbon which comprises firing powdered carbon continuously by feeding powdered carbon into a firing tube and applying microwaves to the top surface of a deposited layer of the powdered carbon so as to form a high-temperature fired layer within the deposited layer.
In another aspect, the present invention provides an apparatus for the continuous firing of powdered carbon which includes a firing tube disposed within a furnace, a powdered carbon feeding device for feeding powdered carbon continuously into the firing tube through one end thereof, a fired product withdrawing device for withdrawing a fired product of powdered carbon continuously from the other end of the firing tube, and one or more microwave waveguides extending into the furnace and serving to apply microwaves to the top surface of a deposited layer of powdered carbon fed into the firing tube and deposited therein, whereby the application of microwaves causes a high-temperature fired layer to be formed within the deposited layer of powdered carbon.